This invention relates generally to methods and apparatus for simultaneously satisfying heating and cooling demands.
Refrigeration apparatus or machines are frequently employed to cool a fluid such as water which is circulated through various rooms or enclosures of a building to cool these areas. Often, the refrigerant of such machines rejects a relatively large amount of heat at the condenser of the machine. This rejected heat is commonly dissipated to the atmosphere, either directly or via a cooling fluid that circulates between the condenser and a cooling tower. Over a period of time, the rejected heat represents a substantial loss of energy, and much attention has been recently directed to reclaiming or recovering this heat to satisfy a heating load or demand.
One general approach to reclaiming this heat is to employ a booster compressor to draw and further compress refrigerant from the condenser of the refrigeration machine. This further compressed vapor is then passed through a separate, heat reclaiming condenser. A heat transfer fluid is circulated through the heat reclaiming condenser in heat transfer relation with the refrigerant passing therethrough. Heat is transferred from the refrigerant to the heat transfer fluid, heating the fluid and condensing the refrigerant. The heated heat transfer fluid may then be used to satisfy a present heating load or the fluid may be stored for later use, and the condensed refrigerant is returned to the cooling circuit for further use therein.
With refrigeration machines having both a cooling circuit and heating circuit as described above, it is desirable to control the heating and cooling circuits to meet varying heating and cooling loads, and it is preferred to control the heating and cooling circuits independent of each other so that variations in one circuit do not affect the other circuit's ability to handle loads placed thereon. However, difficulties arise when the heating and cooling circuits are independently controlled. For example, if the refrigeration machine is called on to simultaneously handle a low cooling load and a high heating load, then the refrigerant flow rate through the cooling circuit is comparatively small and a relatively small amount of vapor is discharged from the compressor of the cooling circuit. At the same time, the refrigerant flow rate through the heating circuit is relatively large and a relatively large portion of the refrigerant discharged from the compressor of the cooling circuit is drawn into the booster compressor and passed through the heating circuit. In fact, under extreme conditions, the refrigerant flow rate through the booster compressor may temporarily exceed the rate at which refrigerant is discharged from the compressor of the cooling circuit. When this occurs, the mass of refrigerant vapor in the condenser of the cooling circuit decreases, decreasing the pressure therein. This, in turn, decreases the pressure at the inlet of the booster compressor. If this pressure falls to a very low level, the temperature of the vapor discharged from the booster compressor may become undesirably high, or the booster compressor may enter what is known as surge conditions wherein there are periodic complete flow reversals in the compressor, destroying the efficiency of the compressor and endangering the integrity of the elements thereof.